Conventionally, there are well known liquefier systems configured to liquefy a raw material gas that is in a gaseous state at normal temperatures and pressures. Examples of the raw material gas include hydrogen gas, helium gas, and neon gas. Such a liquefier system includes: a feed line for feeding the raw material gas; a cooling medium circulation line for causing a cooling medium to circulate; and a heat exchanger for cooling down the raw material gas by means of the cooling medium. While circulating through the cooling medium circulation line, the cooling medium is compressed by a compressor; adiabatically-expanded by an expansion turbine, so that the temperature of the cooling medium is reduced; then the cooling medium exchanges heat with the raw material gas at the heat exchanger, so that the temperature of the cooling medium is increased; and thereafter the cooling medium returns to the compressor.
In such a case where a cooling medium is adiabatically-expanded by an expansion turbine, a bearing is necessary for supporting a rotating shaft of the expansion turbine. If a liquid bearing is applied as the bearing for supporting the rotating shaft, there is a risk that a lubricant such as oil becomes mixed into the cooling medium that passes through the expansion turbine, and thereby the lubricant flows into the cooling medium circulation line. For this reason, preferably, a gas bearing in which the same gas as the cooling medium is used as a lubricant is applied as the bearing for supporting the rotating shaft of the expansion turbine (see Patent Literatures 1, 2, and Non Patent Literature 1).
Gas bearings are roughly categorized into static pressure gas bearings and dynamic pressure gas bearings. The load carrying capacity of a static pressure gas bearing is greater than that of a dynamic pressure gas bearing, and in the case of applying a static pressure gas bearing, friction is less likely to occur between a bearing hole surface and a rotating shaft surface at the time of start-up and stop of the liquefier system. For these reasons, the application of a static pressure gas bearing is more advantageous.